#用递归求n的阶层:n!=(n-1)!*n=(n-2)!*(n-1)*n=1*(n-a)*…..*(n-2)*(n-1)*n
def fib(n):

    if n == 0 or n == 1:

        return 1
    else:
        return n * fib(n-1)

print(fib(7)) 